Taper grinding of artificial filaments



Dec. 419, 1944. F. G. CUNNINGHAM TAPER GRINDING OF ARTIFICIAL FILAMENTSFiled sept. 2, 1943 i Q T v 477-0 fr Patented Dec. I9, 1944 UNITEDSTATES PATENT oFFlcE TAPEB GRINDING F ARTIFICIAL FILAMENTS ApplicationSeptember 2, 1943, Serial No. 500,922

11 Claims.

This invention relates to the taper grinding of artificial filamentsand, more particularly, to the taper grinding of brush bristlescomprising synthetic linear polyamide laments.

Polyamide filaments make excellent brush bristles, especially where thestrength and resilience of the laments has been iproved bymacromolecular orientation through cold drawing. For

use in brushes adapted 'to hold and distribute liquid, such as paintbrushes, it has been found necessary to use ilaments which are tapered.A method of making these tapered filaments is disclosed in United StatesPatent No. 2,292,905. While brushes thus formed are ideal for certainpurposes, and in most uses are superior in toughness, resilience, andabrasion resistance to the best animal and vegetable bristles, certaindifficulties attend their use for painting. For instance, thesesynthetic;A bristles may require comparatively long periods of breakingin before they become capable of distributing paint uniformly andwithout brush marks.

Investigation has shown that these diiiiculties are due to insumcienttaper, particularly at the working end of the bristle. Attempts toincrease the degree of taper of the lament by any method of the priorart to eliminate the above mentioned dilculties, have resulted in thebreaking of the lament or, at best, faulty conguratlon. Orientedpolyamide filaments of configuration and taper suitable for liquiddistributing brushes of the best quality have not-neen produced by anycombination of spinning and drawing methods now known.

An object of the present invention is to provide a synthetic bristlesuitable for use in liquid distributing brushes. A further object is theproduction of oriented synthetic linear polyamide bristles, and brushesof said bristles, of improved liquid distributing characteristics. Astill further object is to .provide a. method and apparatus 'for formingoriented synthetic linear polyamide lamentshaving the above outlinedcharacteristics.` Other objects will be apparent from f 45' thedescription of the `invention given hereinafter.

The above objectsare accomplished according to the present Vinvention bygrinding the working end of tapered oriented synthetic linear polyamidelilaments to increase the taper thereof, and by the use of suchfilaments in brushes adapted to distribute liquid, such as'lpaint. Theinvention further comprises an apparatus whereby. the bristles ofbrushes may be taper ground to improve the liquid distributingcharacteristics thereof.

In order to effect the desired tapering, the tapered oriented syntheticlinear polyamide laments used as the starting material may be held,prior to their assembly into a brush, either individually or as a thingroup, approximately tangentially against a flat moving abrasivesurface. Preferably, however, the taper grinding operation is performedon a completely assembled brush by means of tbe apparatus of thisinvention.

For amore detailed explanation of the invention reference is made to theaccompanying drawing wherein:

Fig. 1 is a section through a tapered synthetic linear polyamidefilament of the type used for brush bristles heretofore and suitable.for use as a starting material in the process of the present invention;

bristle length 0f 3" t0 6", L in Figs. 1 and 2,`

represents about the extreme range of the lament, with the butt diameterD equal to 0.005"

to 0.015". The portion A of the length of the v bristle will equalone-third to two-thirds of L and is. preferably Vof substantiallyconstant diameter throughout, the diameter Di never exceeding thediameter D although the portion A of the bristle may be somewhat taperedso that D1 would be less than D. D2 is the diameter at the working endof theheretofore available tapered bristles, usually from 1/1.3 to V2 ofD.

In Fig. 2 is shown in section a synthetic filament which has been taperground to the configuration of a bristle according to the presentinvention. This bristle is the same as that shown in Fig. 1, except forthe portion B which has been taper ground. B equals one-tenth toonethird of L, and m. the diameter at the working end of the bristle, isless than 0.0025".

It has been discovered that a paint brush in which at least 90% of thefull length bristles have the conguration dened above and shown in Fig.2, is markedly superior to one in which the bristles have theconfiguration indicated in Fig. 1, particularly in that it requiressubstantially no breaking in before becoming capable of distributingpaint uniformly and without brush marks. i

It will be understood that the filament sections shown in Figs. 1 and 2are exaggerated transversely for purposes of illustration. Further, thecross-section through a bristle according to the present invention, neednot be circular but may be elliptical or even quadrangular. Also, thebristles of this invention may be made by taper grinding constantdiameter filament in which case the diameter of the filament will', ofcourse, be constant except for the portion B of its length.

The present invention comprises an apparatus specifically designed totaper grind synthetic laments to the configuration discussed above andone embodiment of that apparatus is illustrated in Fig. 3. A shaft 2 isrotatably mounted in horizontal position in the journal bearings 3--3.This shaft 2 is driven by the electric motor 4, or equivalent powersource, connected to the shaft 2 through the pulley 5 of the motor 4,the drive belt I5, and thev pulley 6 -carried by the shaft 2.

Fixedly mounted on the shaft 2 to rotate therewith are three identicalcrown discs, designated by the reference numeral I, separated from eachother by the smaller discs 1. 'I'he sloping peripheral surfaces of eachcrown disc I meet at an acute angle at the annular apex 8 of each andthese slopes are coated with an -abrasive material 9, such as sandpaper,part way down from the apex 8.

A pair of shafts I2, only Vone of which shows in Fig. 3, are slidablymounted in brackets I3 carried by standards I6. 'I'hese shafts I2 areparallel to shaft 2 and spaced slightly to accommodate a clamp II whichis fixedly mounted on the shafts I2. The clamp II is adapted to hold abrush I securely with the longitudinalY axis ofthe brush vertical and ina plane parallel to and passing through shaft 2, the brush bristles I4extending toward shaft 2 and beyond the coating of abrasive material 9on the crown discs I.

The apparatus is operated by rotating the crown discs I by means of themotor 4 and moving the brush I0 by means of the shafts I2 which slide inthe brackets I3. The crown discs I should be rotated so that they have aperipheral speed of 1,000 feet to 10,000 feet per minute, preferably notless than 6,000 feet per minute. and the brush should be movedtransversely at a speed of 3 to 9" per minute, preferably at about 6"per minute.

As the bristles I4 of the brush I0 come into contact with the slopes ofthe crown discs I, they are picked up and carried slightly upwardly andin the direction of rotation of the shaft 2; the resulting contact ofthe bristles I4 with the abrasive coating 9 on the discs I causes thesides of the lower portions of the bristles I4 to be abraded. When thebristles are picked up by one of the slopes of the crown discs I, theytend to roll over and over and, as they approach the apex 8, they aresuddenly whisked over upon the opposite slope of the crown disc. I'hisaction has the effect of opening up the brush so that the bristles inthe interior are exposed to the action of the abrasive. Observing thelimits of the apex angle of the crown discs, which are highly critical,and the limits of the peripheral speed of the crown discs and thetraversing speed of the brush, it has been found that the brush bristlesremain substantially in order and do not become tangled in thisoperation. Such a result is highly important for satisfactory tapergrinding of the bristles.

When the brush I0 has been traversed beyond the extent of the crown discunit, the direction of traverse is reversed and the brush is passed overthe unit again in the opposite direction. After the brush has beensubjected to this treatment for about 10 minutes', the direction ofrotation of the shaft 2 is reversed, or the brush is turned around, andthe grinding s continued for another I0 minutes. This procedure resultsin substantially uniform grinding throughout the brush so that a highproportion of the individual bristles have been given the configurationhereinbefore discussed.

As a further refinement of the grinding the brush may be heldapproximately tangentially against a rotating abrasive 'wheel ofapproximately fiat peripheral surface to increase the length of paper ofthe outside bristles.

Whether a single crown disc is used in the apparatus or a unit ofseveral crown discs, as shown in Fig. 3, is not at all critical althougha unit of several of these discs is preferred. But the apex angle of thecrown disc is exceedingly important.and must be between 60 and 80. If anangle less than 60 is employed, excessive tangling of the bristlesresults, while an angle greater than results in the grinding oil of thebristle tip.

The size of the crown discs may be varied widely although it ispreferred to use discs having a. diameter of 6" to 24" and a thicknessof 2" to 4". It has been found that wooden` crown discs which are 2%thick and have a diameter ranging from 6" to 24", with an apex angle of70, are particularly satisfactory, especially when the abrasive coatedportion of the slope of the disc extends less than 2" down from the apexand, preferably, extends half way down the distance of the slope fromthe apex.

Assuming brushes in the usual size range of paint brushes are to betaper ground, it is desirable that the abrasive coated portion of eachcrown disc be less than 2" on a slope and that there extends beyond theabrasive coated portion of each slope a comparatively smooth portionsuch as polished wood. This preferred design promotes side grinding ofthe bristles without end grinding. As a practical matter, it has beenfound that the abrasive coating on the slopes of the crown discs may bevaried from one-fourth to three-fourths of the distance down each slopefrom the apex although usually one-half of the distance down each slopeis most satisfactory if the crown discs are less than 4" in thickness.

The abrasive coating on the crown disc may be sandpaper cut to propersize and shape and fastened to the disc by an adhesive. Alternatively,the slopes of the disc may be coated with an adhesive and, while theadhesive is still tacky, there may be blown or pressed thereon abrasiveparticles of suitable size and sharpness. It is pre-- ferred that theabrasive particles be of such size that they will pass a fiS-mesh screenand be retained on a 55-mesh screen.

The supporting and traversing means for the brush may be varied widely.A simple and efficient device has been shown in Fig. 3, more or lessdiagrammatically, but many other equivalent devices lwill readily occurto those skilled in the art. In the device shown, a plurality of brushesmay be supported and ground simultaneously and asoman this is thepreferred method of carrying out 'the invention. The traverse motionotthe brushholding means may be eil'ected manually or, if desired, bymechanical means capable of giving a non-varying reciprocated motion.The brush should be moved in a line parallel to the axis of rotation ofthe crown discV and `atea constant height.

The brush should be disposed at that height relative to the crown disc,which, in the particular condition obtaining, results in the greatestextent of taper grinding without fusion of the bristles. As the apex ofthe crown disc is advanced upwardly into the brush toward its ferrule,the force with which the bristles are pressed against the crown disc,increases due to the restricted action of the ferrule, and the heat offriction likewise increases. This heat may become sufiiciently great tofuse some of the bristles together, greatly impairing the value of thebrush. There is thus an upper limit to the extent that the brush andcrown disc may safely overlap with a given apparatus under givenconditions of operation.` Itis important that this upper limit beapproached as closely as possible in order that the ground portion (B inFig. 2) be of greatest length. With an apparatus of the type illustratedin Fig. 3, having the specifications given in Example I below, andoperated under the conditions given in Vthat example, the optimumoverlap for a 4" brush is 21/2. It will be apparent that the optimumoverlap in each specific instance will have to be determined by trialbut this can be quickly. and readily done. In any event, it is preferredthat the bristles extend down beyond the abrasive portion of the crowndisc. Y

In order that the taper grinding may be uniform, it is important thatthe length of traverse of the brush be a multiple of the distance between two successive apexes of the crown disc unit, except that this isnot essential when the brush, or group of brushes.' being treated passeson each traverse completely beyond the extent of the crown disc unit.The rate of traverse should be suiiiciently slow so that the bristlesare whisked across theapex of each crown disc by the action of rotationrather than pulled across by the movement of the brush. If the rate oftraverse is too fast, the bristles may become tangled. On the otherhand, too slow a rate of traverse may cause unduly prolonged contact ofthe bristles with the abrasive, resulting in fusion of the bristles fromfrictional heating.1 Ordinarily, the rate of traverse will fall Withinthe range of 3" to 9" perminute while a rate of traverse of 6" perminute is preferred.

The following examples illustrate specic embodiments of the presentinvention:

Example I A paint brush 4" wide and 1" thick is formed of syntheticlinear polyamide filaments 41/2" long having an average diameter at thebutt end (D) of 0.012," (see Fig. l) and a'taper ratio of about 1.5.'I'he particular polyamide involved is formed from hexamethylene diamineand sebacic acid. The apparatus used is that illustrated in Fig. 3. Theabrasive coated crown discs have a major diameter of lll/2", athicknessof 2%", and are separated from each other by discs wide. Theslopes of the crown discs meet at an angle of 70. vEach slope ispartially V covered with sandpaper extending 0.8" down at a speed of 6"per minute for ten minutes after which it is turned around and theprocess is repeated for another ten minutes. Examination undermagniiication reveals that most of the bristles have the desiredconnguration.

This brush is then held approximately tangentially against theperipheral surface of `a at rotating grinding wheel, the point ofcontact of the wheel with the bristles being well above the tip ratherthan at the tips of the bristles. Con-v iguration of the inner bristlesis unchanged. The outer bristles resemble the desired configurationexcept that tapered ground portion (B in Fig. 2) is of considerablygreater'- longitudinal extent. This brush handles well, distributespaint evenly, and exhibits a lesser tendency'to leave brush marks thanbrushes made of highest quality hog bristles.

An exactly similar brush, not tapered ground having a bristleconfiguration similar to that shown in Figure l, has 4poor paintdistributing qualities and requires a long period of breaking in toeliminate excessive tendencies to leave brush marks. An otherwiseexactly similar brush, not taper ground in accordance with thisinvention is treated with a fiat surface grinding wheel.' The taperobtained by such treatment does not comply to the desired conigurationexcept in the case of the outermost bristles of the brush.` The paintingcharacteristics of thisbrush are only slightly better than that of thebrush which has received no treatment.

Example II Exemple Ill A brush 2" wide and 1/2" thick is formed fromuntapered oriented polyamide filaments having a diameter about 0.007,5.The polyamide involved is that formed .bythe reaction of hexamethylenediamine and sebacic acid modified by the addition of a .phenolformaldehyde resin. The brush is ground in' an apparatus similar to thatshown in Fig. 3, except that the major diameter of the disc is 6". Thedisc surface speed is 6,000`feet per minute and the rate of traverse ofthe brush is 6" per minute. After one-half hour the direction ofrotation of the disc unit is reversed and the process is continued foranother half hour. Examination shows that the bristles are tapered forapproximately one-third their length and that the tip end is taperedaccording to the desired configuration.

It will be understood that the above examples are merely illustrativeand that the invention is broadly applicable to taper grinding syntheticbristles. The preferred bristle filaments are those made from.polyamides of the type disclosed in Untied` States patents, 2,071,250;2,071,253; and 2,130,948. These polyamides are prepared from*bifunctional polyamide-forming reactants and contain amide groups as anintegral part of the main chain of atoms in the polymer. It is notessential that the linking group in the polymer chain consists solely ofamide groups; it may also contain other groups such as ester groups.Further, the filaments need not consist wholly of polyamide or modifiedpolyamide polymers. Dyes, pigments, fillers, water-repellents,-plasticizera and other modifiers may be present. Polyamides modified byphenol-aldehyde resins have been found particularly useful. Othersynthetic resin bristles, such as those made from cellulose triacetate,for example, may also be treated according to the present invention.

Certain advantages in handling qualities are thought to be gained by theuse in a paint brush of bristles of more than one diameter or bristlesof more than one length or, preferably, bristles of more than one lengthand diameter. The bristles of different sizes may be arranged at randomor regularly, that is, a brush may have a chisel-like edge, the bristleson the two sides being shorter than those in the center, or the bristleson one side being shorter than those on the ot'. ir. It has been foundthat paint brushes so constructed may be satisfactorily taper groundaccording to the present invention.

An advantage of this invention and, perhaps, its greatest advantage, isthat it provides a practical means of taper grinding paint brushbristles to give a paint brush of improved distribution characteristics.However, another advantage is that the liquid-holding properties of thebrush are increased somewhat by the use of bristles taper groundaccording to the present invention.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beYunderstood that the invention is not limited tothe specific embodimentsthereof except as defined in the appended claims.

I claim:

1. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted shaft, meansfor rotating said shaft, a crown disc axially mounted on said shaft torotate therewith, said crown disc having an included apex angle of60-80, an abrasive coating extending part way down each slope of saiddisc from the apex, and means for holding a brush Vwith its longitudinalaxis at right angles to said shaft and in a plane parallel to andpassing through said shaft. with the brush bristles extending towardsaid shaft and beyond said abrasive coating on said crown disc, saidmeans being slidable parallel to said shaft.

2. An apparatus for taper grinding brushes bristled with artificialfilaments. said apparatus comprising a rotatably mounted shaft, meansfor rotating said shaft, a crown disc axially mounted on said shaft torotate therewith, said crown disc having an included apex angle of 6080,an abrasive coating extending from oneasoman fourth to three-fourths ofthe distance down each slope of said disc from the apex, and means forholding a brush with its longitudinal axis at right angles to said shaftand in a plane parallel to and passing through said shaft, with thebrush bristles extending toward said shaft and beyond said abrasivecoating on said crown disc, said vmeans being slidable parallel to saidshaft.

3. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted shaft, meansfor rotating said shaft, a crown disc axially mounted on said shaft torotate therewith, said crown disc being 6" to 24" in diameter and 2" to4 thick, and having an included apex angle of -80, an abrasive coatingextending from one-fourth to three-fourths of the distance down eachslope of said disc from the apex, and means for holding a brush with itslongitudinal axis at right angles to said shaft and in a plane parallelto and .passing through said shaft, with the brush bristles extendingtoward said shaft and beyond said abrasive coating on said crown disc,said means being slidable parallel to said shaft.

4. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted, horizontalshaft, means for rotating said shaft, a crown disc axially mounted onsaid shaft to rotate therewith, said crown disc being 6" to 24" indiameter a'nd approximately 2%" thick, and having an included apex angleof an abrasive coating extending approximately one-half of the distancedown each slope of said disc from the apex, and means for holding abrush with its longitudinal a s vertical and in a plane parallel to andpassing through said shaft, with the brush bristles extending downwardlyand beyond said abrasive coating on said crown disc. said means beingslidable parallel to said shaft.

5. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted shaft, meansfor rotating saidY shaft, a crown disc axially mounted on said shaft torotate therewith, said crown disc having an included apex angle of 6080,an abrasive coating extending from onefourth to three-fourths of thedistance down each slope of said disc from the apex, a pair ofassociated shafts slidably mounted parallel to said first shaft, andclamp means fixedly mounted on said pair of shafts and adapted to hold abrush with its longitudinal axis at right angles to said first shaft andin a plane parallel to and passing through said first shaft, with thebrush bristles extending toward said first shaft and beyond saidabrasive coating on said crown disc.

6. An apparatus for taper grinding brushes bristled with artificialfilaments, said'apparatus comprising a rotatably mounted shaft, meansfor rotating said shaft. a crown disc axially mounted on said shaft torotate therewith, said crown disc being 6" to 24" in diameter and 2" to4" thick,` and having an included apex angle of 60"-80, an abrasivecoating extending from one-fourth to three-fourths of the distance downeach slope of said disc from the apex, a pair of associated shaftsslidably mounted parallel to said first shaft. and clamp means fixedlymounted on said pair of shafts and adapted to hold a brush with itslongitudinal axis at right angles to said first shaft and in a planeparallel to and passing through said first shaft, with the brushbristles extending toward said rst shaft and beyond said abrasivecoating on said crown disc.

7. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted, horizontalshaft, means for rotating said shaft, a crown disc axially mounted Ionsaid shaft to rotate therewith, said crown disc being 6"' to 24" indiameter` and 2" to 4 thick, and having an included apex angle of 60-80,an abrasive coating extending from one-fourth to three-fourths of thedistance down each slope of said disc from the apex, a pair ofassociated horizontal shafts slid# ably mounted parallel and above saidfirst shaft, and clamp means fixedly mounted on said pair of shafts andadapted to hold a brush with its longitudinal axis vertical and in aplane parallel to and passing through said first shaft, with the brushbristles extending downwardly and beyond said abrasive coating on saidcrown disc.

8. An apparatus for taper grinding brushes bristled with artificialfilaments, said apparatus comprising a rotatably mounted shaft, meansfor rotating said shaft, a crown disc axially mounted on said shaft torotate therewith, said crown disc being 6 to 24 in diameter and 2 to 4"thick, and having an included apex angle of 6080, a coating of abrasiveparticles passing a Li-mesh screen and retained on a 55-mesh screen,extending from one-fourth to three-fourths of the distance down eachslope of said disc from the apex,

and means for holding a brush with its longitudi-V nal axis at rightangles to said shaft and in a plane parallel to and passing throughsaidI shaft,

with the brush bristles extending toward said shaft and beyond saidabrasive coating on said crown disc, said means being slidable parallelof rotation of said crown disc, said disc having an abrasive coatingextending part way `down each slope thereof from its apex and having anVincluded apex angle of -80`, and said brush being positioned so that itslongitudinal axis is at n right angles to the axis of rotation of saidcrown -disc and in a plane parallel to and passing through said axis ofrotation, with the brush bristlesl extending toward said crown disc andbeyond said abrasive coating thereon.

10. Process of taper grinding a brush bristled with artificialfilaments, which comprises moving said brush reciprocally at a speed of3" to 9 per minute past a crown disc rotating at a peripheral speed of6,000 feet to 10,000 feet per minute, in a line parallel to the axis ofrotation of said crown disc, said disc having an abrasive coatingextending part way down each .slope thereof from its apex and having anincluded apex angle of 6080, and said brush being positioned so that itslongitudinal axis is at right angles to the axis of rotation of saidcrown disc and in a plane parallel to and passing through said axis ofrotation, with the brush bristles extending toward said crown disc andbeyond said abrasive coating thereon.

11. Process of taper grinding a brush bristled with artificialfilaments, which comprises moving. said brush reciprocally at a speed ofabout 6" per minute past a crown disc rotating at a peripheral speed ofabout 6,000 feet per minute, in a line parallel to the axis of rotationof said crown disc, said disc having an abrasive coating extending partway down each slope thereof from its apex and having an included apexangle lof 6080, and said brush being positioned so that its longitudinallaxis is at right angles to the axis'of rotation of said crown disc andin a plane parallel to and passing through said axis of rotation, `withthe brush `bristles extending toward said crown disc and beyond saidabrasive coating thereon.

FRANCIS GRAHAM CUNNINGHAM.

